 element library { 
  element book {
   attribute id {text},
   attribute available {text},
   element isbn {text},
   element title {attribute xml:lang {text}, text},
   element person {
    attribute id {text},
    element name {text},
    element born {text},
    ((
     attribute type {"author"},
     element dead {text}?
    ) | (
     attribute type {"character"},
     element qualification {text}
    ))
   }*
  } +
 }
